A. Technical Field
The present invention relates to a lighting device comprising at least one light source and at least one diffusing element.
B. Background of the Invention
Such lighting devices are widely used. For example, such lighting devices are used in motor vehicles, where they may assume the form of a tail light or headlight. At least the backup light and, for example, the brake light are generally located in the tail light or headlight. Recently there has been a design trend to also integrate the directional signal light, for example, into the tail light together with the backup light and the brake light, and/or to integrate the directional signal light, for example, into the headlight.
In one type of conventional lighting device having multiple light sources, a clear glass lens, for example, allows an unrestricted view of all components behind the lens. However, designers of vehicle lights such as headlights, directional signal lights, and/or tail lights, for example, must frequently meet the requirement for a uniform external appearance of these vehicle lights. Thus, with respect to the differently colored lights to be integrated into the headlight, for example a yellow directional signal light and a colorless low-beam light, it is undesirable for this color difference to be externally visible when neither of the lights is switched on. In order to provide lights having multiple light sources, for example lights for general illumination, headlights, directional signal lights, and/or tail lights for vehicles, or other lights for which it is not possible to see all the components behind same, for quite some time lights with headlight covers have been used which have a prismatic design or the like on the exit or incident surface. As a result of the prismatic surface, directional light beams are refracted and/or reflected in various directions from each light source, depending on the particular location on the surface at which the light beam strikes the headlight cover. In this manner the directional light beam is converted to predominantly diffuse light radiation. As a result, the components located behind the headlight cover are not visible, and during operation the light sources essentially have the external appearance of a single homogeneous light source. In contrast, when prismatic headlight covers are used it is disadvantageous that their manufacture is complex, since a specific surface structure must be impressed during casting. Furthermore, in many cases a prismatic headlight cover is not desirable from a design standpoint because, for example, a uniform appearance of the headlights and body is preferred.
An improved form of a generic lighting device is disclosed in DE 198 18 009 C2. The cited document describes a multilayer cover for multifunctional tail lights for onroad vehicles. The cover is composed essentially of a three-dimensionally deformed plastic film and at least one reinforcement layer made of plastic which has been extrusion molded onto the three-dimensionally deformed plastic film. One characteristic of these known covers is that the plastic film is designed as a light diffusion plate. In this manner the complex manufacture of light-diffusing optical elements integrally molded in one piece to the interior of conventional light covers is avoided. According to the disclosure, the light diffusion plate may be made of polycarbonate, for example, in which spheres or hemispheres in the form of homogeneously dispersed diffusing pigments are embedded. In this respect, the cover disclosed in the cited document is an improvement over the prismatic headlight covers described in the preceding paragraph above. However, one disadvantage of the device disclosed in the cited document is that once again the manufacture of the proposed multilayer design is complicated, since it requires a method for producing multilayered structures. Since according to Claim 4 of the cited document it is proposed that the layer of the plastic film provided as a light diffusion plate has a thickness of 50 to 700 μm, it is disadvantageous that a reinforcement layer must necessarily be applied for achieving the structural strength required for the headlight cover.